Low power consumption is absolutely critical in digital electronic applications that use batteries as a power source and in most of these applications current drawn while in a sleep mode dictates the battery life of the application. Thus, it is critical to have a very low current drain while in the sleep mode and a low power way to wake up from the sleep mode in a timed manner. Existing wake-up timers that are based on traditional oscillators consume too much power for most lithium battery applications and may consume several microamperes of current. One solution was to use a resistor capacitor (RC) timer that woke up the digital circuit, e.g., digital processor, on a “wake-up on change” event, however, existing digital input structures consume high crowbar currents with a slowly changing input signal.
For some applications it is desirable to have a variable wake-up period that can be controlled with a digital processor.
In battery operated applications a low power programmable low voltage detection (PLVD) circuit is highly desirable but is often omitted due to price and power considerations.
Low power wake-up timers use passive resistor-capacitor timing circuits having slowly rising voltage levels that go toward VDD. The problem with these types of timer circuits is that a leaky capacitor when used in a low power mode (high resistor value) may never wake up the device when the leakage current of the capacitor and the input leakage into the device connection exceeds the drive capability of the resistor. This problem may be aggravated at high temperatures, thus making operation of this type of timer unpredictable.
Therefore, what is needed are ultra-low power programmable timer and low voltage detection circuits that consume very little power and are accurate and reliable over the entire useful temperature range of a device.